Oyster mushrooms are probably one of the most ubiquitous mushrooms around! Even non-foragers are usually familiar with oysters; they're like a step up from "button mushrooms" at the grocery store. Different species grow worldwide and thrive in both wild and cultivated settings. They're simple to learn, reasonably easy to find, usually abundant, and taste pretty good!
Our oyster mushrooms in the lower elevations of Colorado can fruit as early as March during warm winters! Typically, April and May are the more common months to start finding them. They often share habitats with morels though they grow on different substrates! Oyster mushrooms are saprobic, meaning they get their energy and nutrients by feeding on dead and decaying organic matter, unlike mycorrhizal fungi, which get their nutrients from an association with living plants. Therefore, oyster mushrooms will always grow from dead or dying wood. Often, these are stumps or logs, but they can occasionally be buried roots or dead-standing snags!
In Colorado, we have a couple of species of oyster mushrooms, the most common being Pleurotus pulmonarius. We also have aspen oysters, P. populinus, which predominantly grow on the wood of quaking aspens. All of our oysters will be found growing in shelf-like clusters from dead or dying wood. Their caps are off-set and fan or shell-shaped, and their gills are decurrent, running down the off-center stem if present. Oyster mushrooms have a unique odor best described as "oyster mushroom", but that won't make sense until you know it! Often people report them smelling slightly fishy or seafoody, and it's also often compared to anise. Once you find and smell some, you will know the oyster mushroom smell! Note - you could be "that weirdo" and go to your local fancy grocery store to give them a sniff if you've never smelled them before. I suggest you buy those mushrooms with our current state of affairs as they are... even better, buy them and sniff them at home!
As mentioned above, oyster mushrooms can start fruiting in Colorado as early as March and can continue to fruit all summer if conditions remain good for them! Most oyster mushrooms are found in the low elevation riparian and suburban areas growing from cottonwoods, willows, elms, and other hardwoods. We also have the higher-elevation aspen oysters, though I don't see these as often as their low-elevation relatives. Oysters can also sometimes be found growing from coniferous logs in the mountains. I'm not sure which species these are, and they aren't prevalent.
To find oyster mushrooms, you must look for downed logs or stumps and dead trees! In much of the lower elevations, this usually means riparian areas, the same areas where you'll be looking for morels. However, you're not limited to riparian areas; pretty much any dead hardwood is fair game for the oysters! I've found them fruiting on large fallen branches from urban cottonwoods, logs thrown in slash piles, old windbreak stumps, and even on random trees seen while driving around town! Oysters like to fruit out of cracks in the bark, crevices or nooks in logs, and at the base of stumps. They grow exceptionally fast, so if you find some baby oysters feel free to leave them for a day or two before harvesting! I prefer eating smaller oysters, from a quarter up to about palm-sized, but even the largest ones that aren't too buggy can be eaten or dried and ground into mushroom powder.
When I harvest oyster mushrooms, I carefully cut them from their base, trying not to damage the substrate they're growing from too much. Sometimes this is difficult when they're growing between the bark, like in the above photo, so having a small sharp knife and taking your time is a good idea! Harvesting like this usually results in a lovely bunch of oysters still attached to each other. When you get them home, you can separate the individual caps, trim off any tough spots or debris, and then prepare them however you like! Commonly they're just sauteed in butter with some salt and pepper. They're also really great breaded and fried! They can be used in pretty much any recipe that calls for cooked mushrooms, and they have relatively stout flesh, so they can stand up to longer cook times as well! I don't usually preserve oysters, but I've read that they freeze pretty well. You could also dehydrate them if you prefer.
Oysters are a great species for beginner mushroom hunters because there are no close look-a-likes in Colorado. You can quickly and safely identify oysters if you check for all the previously listed traits! As always, be sure to double-check your identification and feel 100% confident in it before consuming any wild foods.
One final interesting note is that there have been one or two reports of golden oysters in Colorado. The one that specifically comes to mind was found at the Denver Zoo in 2018. Golden oysters are a species that have "escaped" from cultivation and naturalized in much of the Eastern and Midwestern states. They could very well become more established in Colorado, so if you find some, make a note of the location, collect them, and consider sending a specimen to the Sam Mitchel Herbarium of Fungi at the Denver Botanical Gardens! They're also delicious, so keep some for yourself too!
In Summary:
Oysters, Pleurotus spp.
The most common species in Colorado is P. pulmonarius.
Found starting as early as March and will fruit through the summer.
Grows from dead or dying hardwoods, often cottonwood, in shelf-like clusters.
Caps are fan or shell-shaped with off-center stems and decurrent gills.
"Oyster mushroom" smell is sometimes described as fishy or faintly of anise.
Typically found in low-elevation riparian areas, but P. populinus grows from aspens at elevation.
I hope you get to find some oysters of your own this spring! Good luck and happy foraging!
-Orion